Electrical protective apparatus



F. R. PARKER.

ELECTRICAL PROTECTIVE APPARATUS.

APPLICATION EILID MAILS, 1907.

RENEWED IAN. 8. 1920.

Patenteil Aug. 24, 1920.

f n. 7 gy Y H a L M L E FP INVENTOR.'

UNITED STATES PATENT OFFICE.

FREDERICK R. PARKER, OF CHICAGO, ILLINOIS.

ELECTRICAL PROTECTIVE APPARATUS.

Application led March 8, 1907, Serial No. 361,354, Renewed January 8,1920.

To all whom t may concern Be it known that l, FREDERICK R. PARKER, acitizen of the United States or' America, residing at Chicago, in thecounty of Cook and State or' Illinois, have invented new and usefulElectrical Protective Apparatus, of which the following is aspecification, reference being had to the accompanying drawinvs,illustrating the invention.

ltfy invention relates to apparatus and devices for protectingrelectrical circuits and apparatus from injury from abnormal electricalcurrents and charges, and in particular to such apparatus employinghigh-potential electricity arresters and thermal protectors commonlyknown as sneak current protectors.

The principal objects of my present invention are,-to provide improvedand simplified apparatus and devices, and parts thereof, of thecharacters herein set Jforth; to provide an improved, simplified, andhighly efficient electro-thermal protector; to provide improvedheat-susceptible material in electro-thermal protectors; to provide animproved high-potential electricity arrester; to provide an improveddielectric for the high-potential electricity ari-esters; to provide animproved unitary protective device comprising electrothermal mechanismand high-potential electricity arrestingr mechanism, and improvedcooperation ot such a device with the protective apparatus; to providean improved arrangement of the electrothermal protective devices andtheir corresponding high-potential electricity arresters, relatively toeach other; to provide an improved arrangement ot' terminals for suchapparatus; and to provide an improved mounting plate or ground plate forsuch apparatus. Other objects will be apparent .trom the followingspecification.

By reference to the accompanying drawings illustrating the preferredforms of my invention,-

Figure l is a plan view of a pair of duplicate sets ot the protectiveapparatus, similarly arranged on and with respect to opposite sides ofthe mounting plate, an alarm arrangement being shown on the right indotted lines and an operating spring being Specification of LettersPatent.

Patented Aug. 24, 1920.

Serial No. 350,249.

5 and G are side views ot preferred forms ot the improved dielectries.tor the arresters; Fig. 7 is a plan view of a modified form of thermalprotector and arrester electrode, with portions shown in cross-section;Fig. 8 is a longitudinal cross-sectional. view ot a portion ot amodified form ot arrester electrode having provision for accommodating athermal protector' at one end thereof,- and Fig. 9 is a front edge viewor" portions of two sections ot one form of the improved protectormounting plate, showing the sections secured together end to end and theimproved means employed in securing the sections together.

Like characters refer to like parts in the several figures.

The protector mounting plate ot Fig. l is preferably made ot two fiatsheet-metal plates l l secured together preferably as shown. Each platel may be ribbed as at 2 to stiften the mounting plate and provide stepsfor the inner or grounded electrodes 3 3 ot the high-potentialelectricity arresters or lightning arresters, if desired. The mountingplate l l is preferably grounded. The .mounting plate is preferably madein tions which are secured together preferably as shown in Fig. 9. Aportion ot the end ot one plate 1 ot each section is eut off as shown at4L 4, or the plates ot each section are assembled out of completeregister with each other, so as to allow the end portions of two ot theplates l l ot the respective adjacent sections to overlap and form ajoint in the mounting plate as at 4. Mounting strips 6 6 for the groundplate may be placed on opposite sides of the overlapping ends ot theplates l. l secured to the plate l 1 and the latter secured together bybolts Gli) 5 which eXtend through the strips 6 6 and the overlappingends of the plates l l. By means of the strips 6 G the mounting' plate ll may be mounted vertically, or in any other desired position, to asuitable support. it Will be seen that the sections of the mounting`plate l l are constructed so that any one, or all, of a series of thesections may be turned end for end if desired.

l preferably mount the protective apparatus on both sides of themounting plate l il, in duplicate sets, as shown in Fig. l, but it maybe mounted on one side only of plate l l it desired. Spring members .7'T' leading to the line conductors, and S leading to the switchboard,(in telephone systems) or to circuits to be protected, are mounted ontoplate l l, pre'lerably near the rear edge thereoii, by bolts 9 l), andare suitably insulated from cach other and from theplate l l byinsulation l). rlhe tree end et each line spring` 7 holds a lightningarrester, comprising` electrodes 8 and ll and an interposed dielectriclf2 in place against the ground plate l l. preferably as shown.Underneath each electrode '3 may be a .strip i3, riveted to the plate ll by rivets lil la which also hold the two halves of the mounting platel 'l together. rlhe strips i3 l5 lit in grooves in the electrodes 3 3 tokeep same in alinement With the apparatus. llach spring 7 is providedwith stops l5 l5 to limit the insertion of the outer electrodes ll 'ilinto the apparatus. Each spring` Y is 'adapted to bear against the mainbody portion of its electrode ll at the outer end or the latter, asshown at 16 in Fig. 2, the spring 7 being bent away trom the electrodell at l? so to bear against the electrode at both ends thereof' only andthereby hold the electrode 3 tightly against the ground plate and theelectrodes l and ll tightly against the dielectric l2 throughout itslength.

rl`he outer end of each electrode ll, which electrode is preferably madeot carbon or other suitable material, is preferably provided with acylindrical extension ld as shown in erspecti;fe in Fig. et. T hiseXtension or element 1S is the heat-producing means of theet-:cess-current thernraf` protcctor. A metal cap 19, provided with acentral stem 20 and slit as at 2l 2l so as to firmly `grip the portion1S andvinalre goed electrical connection therewith, is 'forced onto theend of the portion 18 far enough to adjust the resistance of 18 betweenthe cap 19 and the end 22 olf electrode 1l to the desired amount, and isthere firmly cemented in place by a suitable cement so as to providegrood conductivity between the partsllS and 19. rilhe edges at the slits2l 2l may be turned in slightly it desired, so as to firmly engage theportion 18. The cement may be applied around the sides oli 1&5 or at theend in some instances it has been found that certain homogeneousresistance rods or elements, in the nature oi a solid pie ot material,are objectionable as heating elements in electrothermal protectors,because the resistance thereof varies considerably upon repeated heatingwith various rurrents. have found that the resistance et such heatingelements, or resistance elements, can be kept very uniform, thuseliminating; the above objections, by first heating the element with afcurrent larger than the rents to be sent through it thereafter, andloa'\,'ingl the said larger current in the element longer than smallercurrents will remain therein thereafter. ln other words the resistanceof such a heating element or resistance element can be kept practicallyconstant by lirst electrically heatin` the element to a greater cxtentthan it will afterward be heated in the use of the device. The largercurrent s the resistance ot the elenient'to a cfrA value, which valuewill not be materially changed by lesser currents ,Liassingy,l thro 'dithe element ifor a shorter period ol time. il still larger current mayset tl e resistance of the element to a new value. ie liati-ip` elementi8 oli my invention preiierably treated as above described, beiore thecap l) is cemented in place. llfhen the cap is being cemented in pla e,the resistance oi lo is measured while the cap l) is being pre edthereon, the cap 'l'beinpv pressed onto the e element 1S until theresistance ot the latter adjusted to the proper amount, in whichposition the cap 19 is cemented in place. After the cap l5) is suitablycemented in place, the exposed suriiace or' the portion liz; may beshell-ached ll over to protect it from atmospheric conditions andinsulate it 'from conducting particles and objects 'which mightotherwise vary its resistance. By this construction and treatment theresistance of the heating element i8 may be readily adjusted to theproper amount and lrept practically constant.

The free end of spring` 8 is cut away as shown at 2e and is providedwith suitable contacts 25 25 adapted to bear against the flat surface2G` oi' cap 19 to 'make electrical connection therewith. A. sleeve olZheat-susceptible insulating r ateri al 27 is placed over pin 2() andthrough the opening 24 so as to hold the spring 8 in set position asshown in Fig. l. 1n setting the apparatus, spring 8 is iirst pressed tothe position shown in Figs. 1 and 3, the biiurcated end portionstraddling thc pin 20, and than the sleeve 2T is placed over the pin 20,extending through the opening of spring 8 and thereby holding the latterin set position. The opening 211 is pre terably i'iarrow at 2S so thatthe end portions oi spring S will hold against the sleeve 2T and at thesame time reely move past the pin 20 when the sleeve 27 is sottened orremoved. The sleeve 27 is preferably in'ovided with a head thereon iorconvenience in handling. The heatsusceptible material 27 preferablybecomes softened at a lower temperature than does the cement whichsecures the cap 19 to the portion 1:8. For the heat-susceptiblematerial. 27 l may use sealing wax, bees-wax, paratlin, sott glass(where a heat-susceptible insulating non-inflammable material isrequired), or various other materials. 1n some instances it is verydesirable to employ a heat-susceptible insulating non-infiammablematerial in electrical protectors, to avoid lires which may be caused orhelped along by iniannnablc material, and l desire it to be understoodthat l wish to claim such material broadly in connection. with thisinvention, for all uses with electrothermal protectors and with allkinds of electrothermal apparatus except as dielertrics .forbiglipotential electricity arresters the use as which is claimed broadlyin my United States Letters Patent No. 1,179,380, dated April 11, 1916,on high-potential electricity arrester, being transferred thereto tromthe present application.

In the ,lightning arrester, comprising the electrodes 3 and 11 and thedielectric 12, 1 preferably employ a heat-'susceptible dielectric withnotched edges, as shown in Figs. 5 or (3. lhere the dielectric ol" F ig.(S is used, the notchei'l edge'l is placed'downwardly so as to allowparticlesl ot' carbon which may be broken of by the discharge throughthe arrester, or particles of disintegration to fall `from the arrester,thereby making the arrester self-cleaning. The discharge tl'lrough thearrester preferably passes J[rom one electrode to the other through thenotches in the dielectric 12 or 12. 'Vhen a continued arc is formedwithin the arrester, the heat therefrom softens the dielectricl 12 or12a which allows the electrodes to come together and stop the arc. 1nsome lightning ar esters it is very desirable to have a heat-susceptibleor softenable dielectric which is non-inhammable, so that lwhen thedielectric is softened ane pressed out from lcetween the elec-A trodesot the arrester it will not burn or start a .fire and cause seriousdamage. As

a dielectric to fill this want 1 preferably employ a thin sheet of softglass, preferably rut away at its edge or edges as shown in l `igs. 5yand 6, or otherwise, to provide openings for or means for accommodatingthe discharge through the arrester. 1f desired, the dielectric may besomewhat smaller than the discharge surfaces of the electrodes, so as toprovide a discl'xarge gap along the edges of the electrodes between thedischarge surfaces. When a'continued arc is formed in the arrester, theglass is softened by the intense heat of the arc and pressed out frombetween the electrodes 3 and 11 by the spring pressure on the electrode11, sutliciently to allow the electrodes 3 and 11 to come together andthereby form ya conductive path through the arrester, thus stopping thearc and the excessive heating.A

1t' it is desired to have an alarm to be operated by the operation of athermal protector, a pair ot springs 30 and 31 may be provided for eachprotector set, to which is connected an alarm 32 and battery 33. 1V henspring 8 operates it bears spring 30 into Contact with spring 31 andthereby closes the circuit of battery 33 through the alarm 32, whichoperates or sounds the alarm 32 to indicate that a protector hasoperated.

For convenience in wiring I preferably arrange both line terminals 34and 35 of a pair of springs 7 7 on one side ot the plate l 1 so thatgthetwisted pair of cross-connecting wires of the ordinary distributing orcross-connectingboard, which are generally subject to change, may bebrought direct to the terminals 34 35 without being divided and carriedto opposite sides of the plate 1 1. l do not arrange the switchboardterminals 3G 36 both on one side of the plate 1 1 because the pairs ofswitchboard wires, being permanently connected to the protectors, can beonce readily divided .and carried to opposite sides of the plate 1 1when the system is being installed. This construction of placing bothline terminals and one switchboard terminal of a pair ot protectors onone side oli the mounting plate 1 1, and only one switchboard terminalof the pair on the other side of plate 1 1, simplifies the manufactureot spring parts and at the same time lnovides the advantages forcross-connecting provided by other protectors in which the switchboardterminals and line terminals are all arranged on respective oppositesides of the mounting plate.

T he operation of a thermal protector of my invention is as follows:

T he thermal circuit through the device is from line spring 7, throughheating element 18, metal cap 19,'and contacts 25 25 to switchboardspring 8. An abnormally large current of electricity traversing thispath, or simply through the heating element 18, causes the resistance of18 to produce heat which is conducted to the heat-susceptible material27 by the metal cap 19, and which softens the material 27. hen thematerial 27 is sufficiently softened it releases spring 8 whichoperatesfrom the set position shown in `Figs. 1V and 8 to the position shown indotted lines at 37 in F ig. 1, and thereby opens the circuit to thevswitchboard. The heatsusceptible material 27 releases spring 8 in thatit allows the portions 28 of spring 8 to cut through or slide throughthe softened material 27. As spring 8 engages cap 19 at contact points25 25 only, very little of the heat is conducted off through spring 8where it would be wasted. Then spring 8 operates it may operate an alarmas described above. After spring 8 has operated, if the abnormal currentis of high voltage it may arc through the lightning arrester to ground.1f the arc continues in` the arrester the dielectric 12 (or 12) willsoften and allow the electrodes 3 and 1l to come together and stop thearc, as above described, thereby grounding the line. lf the abnormalcurrent is not of high voltage it will not arc through the arrester(Thus it will be seen that the lightning arrester grounds the line lwhenit should be grounded, and only when it shouldv be grounded; that is,when a highvoltage current is present inl the circuit. 7 hen theabnormal current is of a low voltage it is not necessary to ground theline, merely opening the circuit to the switchboard being sufficient.

To reset the thermal protector for another operation, the used sleeve 27is removed, spring V8 ispressed back to place as originally, as shown inFigs. 1 and 8, and a new sleeve 27 is slipped over pin 20.

1f a Vhigh-voltage current of electricity comes to the apparatus andforms a continued arc in the arrester 11 12 8, the heat of the arc willbe conducted through parts 18v and 19 to heat-susceptible material 27and willsoften Vthe latter and thereby cause spring 8 to operate asdescribed above. The heatof the arc may alsosoften the dielectric 12andtherebyY ground the line as desired. lf the discharge through thearrester is of smallivolume and short duration, such as a weak stroke oflightning, it will not cause spring 8 to operate, nor ground the line byp olf and operates to open the circuit. This device may be, reset byreplacing the used pin 27,a with a new one, first setting spring 8a tothe position shown.

In Fig. 8 I have shown an electrode 11a with a hole 89 in one endthereof adaptedto receive a heating element for the thermal protector,if it is desired to construct the heating element as a separate piecefrom the electrode. 7ith this construction a continued arc in thearrester will operate the thermally-operable apparatus the same as inFig.y 1.j This feature of causing an arc in the arrester to operate thethermal protector,.is a very desirable one, especially in telephoneprotective apparatus, because it is desired to cut the switchboard offfrom the line when the latter becomes crossed with a high-voltage wire.lith protective apparatus now in use this cannot be depended on.

I do not wishto limit this invention' to all of the particular detailsherein set forth, as many modifications thereof may be made or utilizedwithout departing from the scope of the appendedV claims.

l desire it to be understood that certain features of my invention maybe used apart from other vfeatures of the invention, and also that theymay all be used together, without departing from the scope vof theclaims.

The process of treating electrical resistances to stabilize theirresistance, disclosed in this application, forms the subject matter' ofmy co-pending United States patent application Serial No. 898,559, filedJuly 23, 1920, on process of treating electrical. resistances tostabilize their resistance, which is a division of the presentapplication.

Certain forms of the high-potential electricity arresters and dielectricYmembers therefor disclosed in this application, form the subject matterof my eo-pending United States patent application Serial No. 398,560,filed July 28, 1920, on high-potential electricity arrester, which is adivision of the present application.

The mounting plate disclosed in this application, forms rthe subjectmatter of my lco-pending United States patent application Serial No.100657, filed August 2, 1920, on mounting plate for electricalprotective apparatus, which is a division of the present application.

This invention is a modification of the inventions disclosed in myUnited States Letters Patent No. 1,288,728, dated Aug. 28, 1917., oncombined lightning arrester and thermal protector, and in my UnitedStates Letters Patent No. 1,245,014, dated Oct. 80, 1917, on electricalprotective apparatus, and in my United States Letters Patent No.1,252,942, dated Jan. 8, 1918, on electrical protector.

Certain forms of the high-potential electricity arresters anddielectricmembers therefor disclosed in this application are described and claimedin my United States Letters Patent No. 1,179,380, dated Apr. 11, 1910,on high-potential electricity arrester.

Certain Aforms of sheet-metal mounting plates or grfnind plates forelectrical protective ap )aratus are disclosed in my United States.letters Patent No. 293,802, dated July 11, 1905, on electric protectivea paratus, and in my United States Letters atent No. $02,939, dated Oct.24, 1005, on ground plate for electric protective apparatus, and in myco-pendin0r United States patent application Serial. o. 31,487, filed.lune 1, 1015, on mounting plate for electrical protective apparatus.

Another form of sheet-metal mounting plate or ground plate forelectrical protective ap aaratus is disclosed in my United States ettersPatent No. 968,395, dated I Aug. 23, 1910, on self-cleaning electricalprotective apparatus.

That I claim herein is:

1. In apparatus of the character described, a high-potential electricityarrester comprising a pair of electrodes normally held in separatedrelation and in close proximity to each other by a suitable dielectric,an extension on one of the electrodes adapted to produce heat uponabnormal electrical conditions, a suitable terminal cap on the saidextension, a circuit-controlling spring, and a piece of heat-susceptiblematerial normally holding the circuit-controlling spring in Contact withthe said cap.

2. In apparatus of the character described, a high-potential electricityarrester comprising electrodes normally held in close proximity to eachother, an extension on one of the electrodes adapted to produce heatupon abnormal electrical conditions, a terminal for the said extension,circuit-controlling means, and heat-susceptible material normallyholding the said terminal and circuitcontrolling means in electricalconnection with each other.

3. In apparatus of the character described, a high-potential electricityarrester comprising electrodes normally held in close proximity to eachother, excess-current heat-producing means aside from the arrester butassociated with one of the electrodes whereby an arc in the arresterheats the heatproducing means, circuit-controlling means, andheat-susceptible material normally holding the circuit-controlling meansin circuit with the heat-producing means.-

4. The combination of an electro-thermal protector comprisingheat-producing means and operable mechanism adapted to be operated byheat from the heat-producing means, rand a high-potential electricityarrester aside from the said electro-thermal protector' but associatedtherewith whereby an arc in the arrester heats and thereby causes theoperation of the said mechanism.

The combination of an excess-current protector comprising heat-producingmeans and operable mechanism adapted to be operated thereby uponabnormal current conditions, and a high-potential electricity arresteraside from the said excess-current protector but associated therewithwhereby abnormal electrical conditions in the arrester causes theoperation of the said mechanism.

G. A high-potential electricity arrester comprising suitable electrodes,an extension on one of the electrodes adapted to produce heat uponabnormal electrical conditions, circuit switching means, andheat-susceptible material normally holding the circuit switching meansin circuit with the said extension.

7. A high-potential electricity arrester comprising suitable electrodes,an extension on one of the electrodes adapted to produce heat uponabnormal electrical conditions therein switching means, andheat-susceptible material normally holding the switching means in setrelation to the said extension to be operated by heat therein.

S. A high-potential electricity arrester comprising suitable electrodes,an extension on one end of one of the electrodes, said extension being.adapted to produce heat upon abnormal current conditions, a metallic capfitted on the said extension, an operable spring member, andheat-susceptible material normally holding the said spring member undertension in electrical connection with the said cap.

9. A high-potential electricity arrester comprising suitable electrodes,an extension on one end of one of the electrodes, said extension beingadapted to produce heat upon abnormal current conditions, a metallic capfitted on the said extension, an operable spring member, and a piece ofheat-susceptible material removably engaging the said cap whereby thesaid spring member is held under tension in electrical connection withthe said cap.

10. A high-potential electricity arrester comprising suitableelectrodes, an extension on one end of one of the electrodes, saidextension being adapted to produce heat upon abnormal currentconditions, a metallic cap fitted on the said extension, said cap havinga substantially flat Contact surface and a pin extending therefrom, anoperable spring member provided with a suitable slot at the end thereoffor accommodating the said pin and suitable contacts to engage the saidflat surface of the cap, and a hollow piece of heat-susceptibleinsulating material placed over the said pin and through the said slotwhereby the said spring member is held under tension in contact with thesaid cap, the said spring member moving out of contact with the said capwhen the heat-susceptible material is softened or removed.

11. 1n an electrothermal device having operable mechanism and aresistance heater for causing` the operation ot' the said mechanism,sott glass un der control of the heater and normally holding the saidmechanism from opera-.ting` but permitting it to operate when softenedby heat from the heater.

19.. ln a thermally-operable devicehaving operable mechanism and aresistance heater tor producing heat to cause the operation ot' the saidmechanism, noniniiammabl'e heatsusceptible insulating` material undercontrol of the heater and normally holding the said mechanism fromoperating but permitting it to operate when heated.

13. rllhe combination with electrical protective apparatus adapted toreceive and hold a protective device, ot an electrode ot ahigh-potential electricity arrester and a resistance'heater aside tromthe vsaid electro-de but attached thereto whereby the said electrode andheater constitute a unitary device adapted to be removed from the saidapparatus or replaced therein as a unit, and switching mechanism undercontrol ot the heater.

14. The combination with electrical protective apparatus adapted toreceive and hold a protective device, ot a high-potential electricityarrester and a resistance heater aside from the said arrester butattached thereto whereby the arrester and heater constitute a unitarydevice adapted to be removed trom the said apparatus or replaced thereinas a unit, and switching mechanism under control of the heater.

15. The combination of a high-potential electricity arrester havingelectrodes, and a separate resistance heater carried by an electrode,the said heater having thermally-operable mechanism under its control.

' 16. The combination with a resistance heater having thermally-operablemechanism under its control, of an electrode ot a high-potentialelectricity arrester aside from the said heater but attached thereto.

17. The combination with a resistance heater having thermally-operablemechanism under its control, of a separate highpotential electricityarrester positioned iny close proximity to the said heater wherebyexcessive heating in the arrester heats the said heater sutficiently tocause same to heat the said mechanism to operate it.

18. A high-potential electricity arrester having suitable electrodes, Ya resistance heater aside .trom the arrester but carried by one oi thesaid electrodes and adapted to produce heat upon abnormal electricalconditions, and thermally-operable switching mechanism under control ofthe said heater.

19. lThe combination with electrical protective apparatus comprising aground plate and sets of spring members mounted upon the ground plateand adapted to receive protective devices, of a unitary protectivedevice for each set of spring members, comprising au electrode of lahigh-potential electricity arrester and a separate electrothermal devicemechanically connected together whereby they may be removed trom thesaid spring members or replaced therein as a unit, each saidelectrothermal device having suitable switching mechanism under itscontrol.

20. rlhe combination with electrical protective apparatus comprising aground plate and sets oi' spring members mount-ed upon the ground plateand adapted to receive protective devices, of a unitary protectivedevice for each set of spring members, comprising a high-potentialelectricity arrester and a separate electrothermal device mechanicallyconnected together whereby they maybe removed from the said springmembers or replaced therein as a unit, each said electrothermal devicehaving suitable switching mechanism under its control.

21. The combination with electrical protecti've apparatus adapted tovreceive and hold a protective device, of an electrode ot ahigh-potential electricity arrester and a separate resistance heatermechanicall-y'connected together whereby the said electrode and heaterconstitute a unitary device adapted to be removed from the saidapparatus or replaced therein as a unit, and operable mechanism undercontrol of' the heater.

22. The combination with electrical protective apparatus adapted toreceiveand hold a protective device, of a high-potential electricityarrester and a separate resistance heater mechanically connectedtogether whereby the said arrester and heater constitute a unitarydevice adapted to be removed from the said apparatus or replaced thereinas a unit, and operable mechanism under controlk of the heater.

23. ylhe combination with a resistance heater having thermally-operablemechanism under its control, of a separate electrode of a high-potentialelectricity arrester mechanically connected with the said heater wherebythe latter and the electrode constitute. a unitary device.

24. rEhe combination with a resistance heater having thermally-'operablemechanism under its control, of a separate highpotential electricityarrester mechanically connected with the said heater whereby theV latterand the arrester constitute a unitary device.

25.111 apparatus of the character set forth, a unitary structurecomprising an electrode of a high-potential electricity arrester and aseparate resistance heater attached to each other.

2G. The combination with a high-potential electricity arrester, ofthermally-operable mechanism having a resistance heater for causing theoperation thereof upon an abnormal current in the heater, the latterbeing apart from the arrester but adapted and arranged to transmit heatfrom the arrester to the said thermally-operable mechanism to cause theoperation thereof upon excessive heating in the arrester.

27. The combination with electrical protective apparatus comprising aground plate and sets of spring members mounted upon the ground plateand adapted to receive protective devices, of a unitary protectivedevice for each set of spring members, comprising in its construction ahigh-potential electricity arrester and a separate resistance heateradapted and arranged to be removed from the said spring members orreplaced therein as a unit, each said device having thermo-responsivemechanism under its control.

As inventor of the foregoing I hereunto subscribe my name in thepresence of two subscribing witnesses, this 4th day of March, 1907.

FREDERICK R. PARKER.

W'itnesses WALTER A. GREIG, ROBERT G. PARKER.

